a. Field of the Invention
This invention relates to the field of networked computing. More specifically, the invention relates to the clustering of computers to support a set of remote services.
b. Related Art
An Encapsulated Cluster (EC) is characterized by a Connection-Router (CR) node and multiple server hosts providing a set of services (e.g. Web service, NFS, etc.). An example of a system which provides encapsulated clustering is described in U.S. Pat. No. 5,371,852, entitled "METHOD AND APPARATUS FOR MAKING A CLUSTER OF COMPUTERS APPEAR AS A SINGLE HOST ON A COMPUTER NETWORK".
Remote clients request services from the EC using protocols based, for example, on TCP/IP (e.g. HTTP). The service time for each request varies depending on the type of service, and the availability of the corresponding server applications. Hence, a naive allocation of connections quickly creates a skewed allocation that under utilizes the available EC resources, and introduces unnecessary delay to the requests.
The prior art has shown that there are many performance problems relating to scaling servers. See, for example, NCSA's World Wide Web Server: Design and Performance, IEEE Computer, Volume 28, Number 11, November 1995, Pages 68-74. Consider an EC which uses round-robin DNS to support Web servers (i.e. httpd demons). The servers provide access services to video streams, database queries, and static web pages via http. The service time for each type of request varies widely depending on the type of services being provided, and the actual content involved. For instance, a complex database query could take orders of magnitude more time than providing a static, pre-loaded HTML page. This imbalance in request processing time often causes skewed utilization of the server cluster. Related problems with round-robin DNS are described in User Access Paterns to NCSA's Worldwide Web Server, Kwa et al, Technical Report UIUCDSD-R-95-1394, Department of Computer Science, University of Illinois Urbana-Champaign, February 1995).
The prior art has shown that there is a need for dynamic allocation of resources. See, for example, Evaluating Management Decisions via Delegation, German Goldszmidt and Yechiam Yemeni, The Third International Symposium on Integrated Network Management, San Francisco, Calif., April 1993. An EC provides a single system image of a collection of services, typically over a collection of hosts. However, actual installations may require that services be allocated according to specific user policies, which can be dynamic. For example, a specific subset of the hosts may be allocated for secure transactions on a merchant Web server, while video on demand services is supported by another subset of hosts which include specialized hardware.